Internal combustion engines with direct injection (DI) have a large potential for reducing fuel consumption at relatively low exhaust emission output. In contrast to manifold injection, the fuel with direct injection is injected directly into the combustion chambers of the combustion engine at high pressure.
Injection systems with a common rail are known for this purpose. In such common-rail systems, the fuel pressure, available largely independent of speed and rate of injection and controlled from the electronic control unit of the internal combustion engine by means of pressure sensors and pressure regulators, is built up in the common rail by means of a high-pressure pump. The fuel is injected into the combustion chamber by means of an electrically controlled injector. This receives its signals from the control unit. By means of the functional separation of the pressure generation and injection, the injection pressure can to a great extent largely be freely chosen independent of the actual operating point of the internal combustion engine.
To increase the power and torque of internal combustion engines, a blower device is known that increases the amount of charge by precompression. In this case, a supercharger supplies fresh air to the cylinder(s) of the internal combustion engine. With mechanical supercharging, the supercharger is driven directly from the internal combustion engine (e.g. supercharger charging), whereas with exhaust gas turbo charging a turbine drives a supercharger in the inlet tract of the internal combustion engine.
To reduce pumping losses, modern internal combustion engines have variable valve drives with a single, multi-stage or stepless variability. The variable valve control of the inlet and outlet valves offers the possibility of setting the valve timing more or less as required within the physical limits of the existing actuator principle (mechanical system, hydraulic system, electrical system, pneumatic system or a combination of the named systems). Such systems enable the valve overlap to be set. They are also known as VVT (variable valve timing) or IVVT (infinitely variable valve timing) systems. Variable valve control also enables the valve lift to be set. Such systems are known as VVL (variable valve lift) systems.
Reduced consumption, reduced untreated emissions and a higher torque can be achieved by using variable valve drives.
The exhaust emissions of an internal combustion engine can be effectively reduced by catalytic re-treatment of the exhaust gas using an exhaust gas catalyst in conjunction with a lambda control device. An important precondition for this is, however, that in addition to the lambda probe of the lambda control device, the catalyst must also have reached its light-off temperature. Below this temperature, the exhaust gas catalyst has little or no effect and reaction takes place only at sufficiently low conversion rates.
To ensure that the light-off temperature is quickly achieved and the exhaust emissions still reduced during the cold-start phase of the internal combustion engine, during which 50–90% of the complete emissions are output within the first 10–20 seconds, various warm-up strategies are known.
In systems with exhaust gas turbocharging, achieving the catalyst light-off that is optimum for emissions is critical due to the heatsink through the exhaust gas turbine. Secondary air systems are frequently used to limit the cold-start emissions.
To do this, for example, secondary air is blown in close to the exhaust valves by means of a secondary air pump during the warm-up. Due to the reaction of the blown-in air with the unburned exhaust gas constituents contained in the hot exhaust gases and the further oxidation in the catalyst, this is heated up more quickly.
DE 44 41 164 A1 describes a device for controlling the charge-air flow for a supercharged internal combustion engine, where the secondary air is not supplied from a separate secondary air pump but instead from a supercharger, provided in any case for the supply and compression of the charge-air. The charge-air is supplied to the internal combustion engine via a charge-air line, with a throttle valve being fitted in this charge-air line. Upstream of the throttle valve and downstream of the supercharger, a circulating air line branches off to the suction side of the supercharger. A circulating air actuator is fitted in the circulating air line. A connecting line leads from the pressure side of the supercharger to an exhaust gas line of the internal combustion engine, with a regulating valve connected to an engine control unit being fitted in this connecting line. To realize a wide operating range of the internal combustion engine with an optimum supply of secondary air to achieve the best possible exhaust gas values, it is suggested that this branch of the connecting line be arranged in the charge-air line upstream of the circulating air line.
From DE 44 45 779 A1, a method is known for the control of a multicylinder internal combustion engine in the cold-start and warm-up phase. The gas charge cycle in the individual cylinders of this internal combustion engine takes place via inlet devices, at least for the air and outlet devices for the exhaust gas, that can be controlled independently of each other but with opening times and closing times that can be harmonized to each other. Starting in the cold-start phase and continuing up to the warm-up phase, the fuel is supplied only to one part of the cylinders and the supply of fuel to the other part of the cylinders is switched off, and they then operate as compressors and the amount of air heated in these cylinders by the compression process is fed via the outlet device into the exhaust gas system for the after-reaction of the exhaust gases.